Design of a wind tunnel for plug seedlings production under artificial lighting

A wind tunnel consisting two air flow conditioners with polycarbonate pipes, a plant growth room, a suction fan and a fan controller, and fluorescent lamps, was newly designed to investigate the interactions between the growth of plug seedlings (plugs) under artificial light and their physical environment. Measurements showed a uniformity in the vertical profiles of air current speed at the middle and rear regions of plug trays in wind tunnel. Maximum air temperature was often observed near the top of a stand of plugs. Since Richardson number was ranged from -0.07 to +0.01, the atmosphere over a stand of plugs in wind tunnel was in an unstable or near-neutral stability state. Eddy diffusivity (KM) at air current speed of 0.9 m s^-1 was about two times as many as that at air current speed of 0.3 m s^-1. (K _M) at the rear region was 1.6 to 23.1 % lower than that at the middle region. The wind tunnel developed in this study would be useful to investigate the effects of air current speed on the microclimates over and inside a stand of plugs and to collect basic data for a large-scale plug production under artificial light in a semi-closed ecological system.